An SSD (Solid State Drive) includes multiple flash memory chips that serves as nonvolatile semiconductor memory, a controller for carrying out read/write control of the flash memory chips as required by the host device, a buffer memory between the flash memory chips and the host device, a power supply circuit, an interface to the host device, and so on.
Power supplied by an external power source may cut off abruptly without previous notice while the SSD is in use. When this happens, any volatile data that may be present in volatile memory must be stored persistently. Therefore, the SSD has a backup power source such as a battery, a capacitor, or other similar backup system to guard against loss of data stored in the volatile memory during outages.
A capacitive backup power supply often is capable of supplying electric power for an extremely short time, between roughly 10 ms and 0.1 sec. Therefore the data stored in the volatile memory should be processed within a time as short as possible during outages.